Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/15/2000
Publication Date: N/A
Interpretive Summary: NA
Technical Abstract: At present very little is known about the protist Helicosporidium sp., a pathogen of insects, mites, cladocerans and trematodes. Historically, this pathogen was first detected in a certopogonid and described by Keilin in the early 1900s. Kudo (1931) placed it in a separate order Helicosporidia within Cnidiospora. In the 1960s, Weiser, examining both type material and a new isolate from a hepialid larva, proposed that this organism should be transferred to the Ascomycetes. Later studies by Lindegren and Hoffman (1976) proposed that the developmental stages of this organism were closer to the Protozoa than fungi. An Helicosporidium sp. isolated from the black fly Simulium jonesi Stone & Snoddy (Diptera: Simuliidae) has been amplified under both in vitro and in vivo conditions. In order to evaluate the phylogenetic position of this organism, the 18S, 26S, 5.8S regions of the Helicosporidium DNA, as well as some partial sequences of the actin and tubulin genes, were amplified by PCR and sequenced. BLAST analyses were performed and surprisingly, the most significant "hits" suggested similarities with unicellular green algae (Chlorophytae) for all five sequences. These sequences were then aligned with similar sequences from representative eukaryotes and analyzed using maximum-parsimony. Such analyses led to the construction of two phylogenetic trees that evaluate the position of Helicosporidium sp. within the phylogeny of eukaryotes, in regard to its rDNA genes and its nuclear genes (actin and tubulin), respectively. Both trees failed to associate Helicosporidium with any of the sampled eukaryotic taxa. This suggests that Helicosporidium sp. may represent a unique lineage that diverged very early from other major eukaryote clades.